Don't. There's no telling what would actually be going into the body.
I'm considering a premixed pen, even though I know it's not the best option, from someone at a local gym. My brother deals with back problems like bulging discs and surrounding scar tissue. He isn't comfortable handling this himself, so I wanted the simplest entry point possible to get him started and demonstrate the potential upside. That leads me to the premixed pen, but I haven't located any dosing information specific to it, only for individual vials. I'll move him toward those later, yet right now I need something to prove it can help. It's basically a low-commitment test. Any guidance on initial amounts and how often to use them would be appreciated.